It's too bad the SGX didn't get more use. Though I'm guessing it was rather expensive. But if you threw that into the DUO it would have made for a nice combo. I think I recall a thread where someone said that Street Fighter II' one character's graphical animations took up around 128K. Well with the SGX and Super CD-ROM format you might have been able to pull it off since the SGX brings up the work RAM to 64K. And in general the added RAM could have helped with HuCards and using compression since you have a bigger buffer to decompress to. I wonder if any of the SGX titles utilized the extra RAM to use compression to fit more into those HuCards.
It would be fun to see a homemade SGX DUO. I bet it could be done.